Many circuit breakers are operable by a trip coil which, when activated, are energised by a DC voltage supply, typically a battery. It is known to monitor the operation and performance of such circuit breakers by analysing the current which flows through the trip coil when energised. The PROFILE (trade mark) range of products supplied by Kelman Limited of Lissue Road, Lisburn, Northern Ireland, United Kingdom, exemplify circuit breaker analysers of this type.
Usually, a given site, for example an electricity distribution sub-station, has many circuit breakers that require monitoring. It is cost prohibitive and can be technically difficult to install a separate monitoring system at each circuit breaker. Typically, the respective trip coil for each circuit breaker is connected in parallel with a common DC voltage supply and a single circuit breaker analyser is provided for measuring the current at the DC voltage supply.
A problem with this arrangement is that the analyser needs to know which circuit breaker(s) has operated at any given time. Conventionally, this requires a respective electrical connection between each circuit breaker (or an associated component) and the analyser. This is considered to be relatively expensive and can be technically difficult to implement.